Patent GB-296363-A (GB)
Title: Circuit arrangement for telephone installations with main and branch exchanges and selector working
IPC: H04Q3/58
Filed: 1928-03-16
Abstract: 296,363. Siemens & Halske Akt.-Ges. Aug. 30, 1927, [Convention date]. Automatic exchange systems.-In a system in which a single junction VL from a main exchange serves a group of say 10 subscribers at a branch station UV, a relay T is energized during either an incoming or an outgoing call to isolate the branch lines, which are normally connected. to a common call initiating relay An. In the case of an outgoing call the junction switch W acts as a finder, and is stopped by a relay U (in the junction a wire) which is energized over the calling loop. In the case of an incoming call the switch W is set numerically by an additional digit transmitted over the junction b wire; ringing current is then sent over the junction a wire and when the branch subscriber answers the relay U is energized. In both cases the relay U energizes F to complete a loop circuit from the branch substation over the junction VL. The branch battery is charged and the branch lines are fed from the main exchange. Specification 296,424 is referred to. Charging branch battery. An 8-volt battery at the station UV is normally connected in a charging circuit over resistance W2, the a side of junction VL, and upper winding of relay R, which does not respond. Call to main exchange; switch W acts as finder. There are no relays individual to the branch lines, which are all normally connected on the a side to the a side of junction VL and on the b side to upper winding of relay An. This relay is energized over a calling line and the junction a wire and energizes magnet D1 which interacts with relay F to advance the switch W. Relay T is energized in parallel with lower winding of An over off-normal contact d1 and isolates the branch lines. When the calling line is reached, relay U is energized over the junction a wire and energizes F which brings U into a loop with the top and bottom windings of R. Tandem pre-selectors IVW, IIVW. Relay R, which is now energized for the first time, starts the switch IVW to find an idle switch IIVW, whereupon T1 is energized in series with R1, which starts IIVW. When an idle selector IGW is found, T2 is energized in series with C1 and the upper windings of R1, T1. Relay R remains locked to the calling loop over its own contacts (to keep the loop closed for relay U) until the first impulse arrives and then falls back. The connection is completed in known manner. Release. The relapse of relay U, when the calling subscriber hangs up, restores the interaction circuits of magnet D1 and relay F, and the switch W advances to normal, whereupon relays An, T are released. Call from main exchange. The connector LW receives each digit as a series of ground impulses on the a wire while battery is connected throughout the digit to the b wire. The first digit is repeated to vertical magnet H. The sequence switch, controlled by magnet S, then goes to second position, the second digit is repeated to rotary magnet D, and the sequence switch goes to fourth position. Busy test and release. As the third position is passed, a test circuit is closed for relay P to a normal contact of switch IVW. If the junction VL is busy, relay P is not energized, tone is sent back, and on the call being abandoned the release magnet M is energized in fourth position. Selection of wanted branch line by switch W. If the junction VL is idle, relay P is energized in series with T1 and moves the sequence switch to fifth position. Relays C and X at the station UV are energized over the junction b wire from contact 42 of A1, and C energizes An and T to isolate the branch lines. The final digit is repeated by A1 to X (C remaining energized) and by X to D1. Relay G at the main exchange is energized by the first impulse and locks itself, and at the end of the digit the sequence switch goes to sixth position and G is unlocked. Supply of ringing current. Ringing current from RM is sent out over the junction a wire, and when the subscriber answers relays U1, U in the ringing circuit are energized. Relay U1 sends the sequence switch to its seventh (conversation) position and is cut out. Relay U energizes F which cuts out C and X and completes a loop circuit over the junction to relays A1, B1, which now act as a feed-bridge. Release. When the called subscriber hangs up, the sequence switch of the connector LW goes to its tenth position, and the switch W is restored as previously described. When the calling subscriber also hangs up, the connector release magnet M is energized, and on the restoration of the connector the sequence switch goes forward. to its first position.